1. Field of the Invention
The present invention relates to soft magnetic films for applications such as main pole layers in perpendicular magnetic recording heads, and particularly to a soft magnetic film formed of a CoFeNi alloy with reduced film stress and a magnetic head including the soft magnetic film.
2. Description of the Related Art
Soft magnetic films for applications such as main pole layers in perpendicular magnetic recording heads are required to have high saturation flux densities. Among such soft magnetic films with high saturation flux densities are CoFeNi alloy films, which have higher saturation flux densities than, for example, NiFe alloy films.
For example, U.S. Patent Application Publication No. 2004/0053077 A1 (Patent Document 1) discloses an invention related to CoFe alloy (no description for CoFeNi alloy). According to Patent Document 1, saccharin sodium, which is generally added to a plating bath, is not added so that the saturation flux density of CoFe alloy can be increased. Saccharin sodium is used to reduce film stress; if saccharin sodium is not added to a plating bath, the resultant film poses problems such as increased stress.
The problem of increased stress results similarly for plating with CoFeNi alloy in a plating bath containing no saccharin sodium.
Japanese Unexamined Patent Application Publication No. 11-86217 (the English translation of Patent Abstracts of Japan (PAJ); Patent Document 2) is intended to produce a magnetic film having higher high-frequency characteristics by adding thiourea to a plating bath so that the magnetic film can contain sulfur to achieve higher resistivity. Patent Document 2, however, makes no mention of the stress of a soft magnetic film, and the addition of sulfur cannot be expected to provide higher saturation flux densities and corrosion resistance.
As described above, minimizing the sulfur content of a soft magnetic film can be expected to provide, for example, higher saturation flux densities and corrosion resistance though the minimized sulfur content also causes the problem of increased film stress. Such increased film stress is undesirable because, for example, the soft magnetic film peels off more readily.
It is known that a soft magnetic film contains impurity elements. The impurity elements are believed to have no significant effect on the soft magnetic characteristics of the film because the impurity elements are contained in trace amounts (for example, at the ppm level); conventionally, the concentration ratios of the impurity elements are not controlled.
Table 1 of Patent Document 1, for example, discloses the compositions, saturation flux densities, film stresses, etc. of CoFe alloys in Examples 1 and 2. The CoFe alloys of Examples 1 and 2 have high saturation flux densities, but exhibit significant variations in film stress; particularly, some of them have film stresses exceeding 1,200 MPa. Such variations in film stress are also found among soft magnetic films having similar Co and Fe contents.